Every once in a while you will see somebody swirl their glass of wine, raise it towards the light and watch with bated breath for the wine’s legs to appear, a mythical indicator of wine quality. These legs, or splits as the French describe them, are the streaks of wine forming on the side of the wine glass. The legs were when thought to be associated with a wine’s quality (the more legs, the greater the quality). However, the legs have more to do with physics, the wine’s surface tension and alcohol content, than viewed quality.
Wine is a mix of alcohol and water, the alcohol has a quicker evaporation rate and a lower surface stress than water, successfully requiring the alcohol to evaporate at a quicker rate. This vibrant allows the water’s surface area tension and concentration to enhance, pushing the upper hands the glass up until the surface tension presses the water into beads. Lastly, gravity wins the fight and requires the liquid to tear down the glass in a beat streak. Still not persuaded that it’s physics and not quality that drives this phenomenon? Try covering your next glass of wine and see if the legs present substantially lower when covered compared to when open. No evaporation, no legs. Enjoy none the less.